Integrated lateral short circuit for a beneficial modification of current distribution structure for xMR magnetoresistive sensors

ABSTRACT

The invention relates to a magnetoresistive device formed to sense an externally applied magnetic field, and a related method. The magnetoresistive device includes a magnetoresistive stripe formed over an underlying, metallic layer that is patterned to produce electrically isolated conductive regions over a substrate, such as a silicon substrate. An insulating layer separates the patterned metallic layer from the magnetoresistive stripe. A plurality of conductive vias is formed to couple the isolated regions of the metallic layer to the magnetoresistive stripe. The conductive vias form local short circuits between the magnetoresistive stripe and the isolated regions of the metallic layer to alter the uniformity of a current flow therein, thereby improving the position and angular sensing accuracy of the magnetoresistive device. In an advantageous embodiment, the metallic layer is formed as electrically conductive stripes oriented at approximately a 45° angle with respect to an axis of the magnetoresistive device.

TECHNICAL FIELD

An embodiment of the invention generally relates to magnetoresistivesensors, a process for producing a resistance dependent on an externallyapplied magnetic field, and a related method.

BACKGROUND

To sense the position, velocity, or orientation of a physical object, anelectrical sensor frequently relies on a change in a magnetic field,which can be sensed by a variety of techniques. One technique utilizes aHall-effect sensor, which relies on a potential difference created onopposite sides of an electrical conductor. The potential difference iscreated by an externally applied magnetic field perpendicular to acurrent flow within the sensor. Another utilizes a loop of wire, relyingon Faraday's Law, to create a voltage proportional to a rate of changeof a magnetic field enclosed by the area of the loop. A third techniquerelies on the magnetoresistive effect, which is the property of amaterial to change its electrical resistance in the presence of anexternally applied magnetic field. Although these techniques have beenapplied in a range of applications, their low sensitivity to anexternally applied magnetic field or issues related to low-costmanufacturing have stimulated ongoing research to identify improvedfield-sensing methods.

Various research efforts have focused on devices exhibiting amagnetoresistive effect. The “anisotropic magnetoresistive effect”(AMR), discovered by William Thomson in 1856, produces a small change inthe electrical resistance of certain conductors in the presence of anexternally applied magnetic field. Recently discovered variations ofthis effect produce a greater relative change in electrical resistance.One resistance-altering effect is referred to as the “giantmagnetoresistive effect” (GMR), which is a quantum mechanical phenomenonobserved in thin films formed of alternating ferromagnetic andnonmagnetic metal layers. Another is the “colossal magnetoresistiveeffect” (CMR), which is a magnetic property of some materials such asmanganese-based perovskite oxides. A third is the “tunnelmagnetoresistive effect” (TMR), which occurs when two ferromagnets areseparated by a very thin (˜1 nm) insulator. Collectively, thesemagnetoresistive effects can be referred to as xMR.

Magnetoresistance is a general property of a material whereby itselectrical resistance is dependent on the angle between the direction ofan electrical current flow within the material and the direction of anexternally applied magnetic field. The resulting electrical resistanceis generally a maximum when the current flow and the externally appliedmagnetic field are parallel. To produce an electrical resistance with alinear dependence on a change of the direction of the externally appliedmagnetic field, conductive stripes, typically aluminum or gold, aredeposited on the surface of a thin film of an appropriatemagnetoresistive material, such as Permalloy, at an angle inclined to aconductive axis of the device by about 45°. Such a structure is oftenreferred to as a “barber pole.”

The current distribution within a stripe of an xMR material is roughlyuniform over its width, which is usually not the optimal arrangement incertain sensor applications. In order to obtain efficient sensorperformance, an xMR stripe is generally formed with a very wide lateraldimension with respect to current flow (e.g., for angle-sensingapplications) or with a very narrow lateral dimension (e.g., for rotaryspeed-sensing applications), which is disadvantageous in view of sensorsensitivity, size, and manufacturing process controllability.

Thus, a challenge in designing a sensor utilizing a stripe of an xMRmaterial to sense a position, velocity, or an angle of a physical objectis generating a reliable resistance change in the sensor with sufficientrepeatability, magnitude, and accuracy for the application, and with lowcost.

SUMMARY OF THE INVENTION

In accordance with one exemplary embodiment of the invention, amagnetoresistive device and a related method are provided. Themagnetoresistive device further includes a substrate, a metallic layerformed over the substrate, an insulating layer formed over the metallicstructure, a magnetoresistive stripe formed over the insulating layer,and a plurality of conductive vias coupling the metallic layer to themagnetoresistive stripe. In an advantageous embodiment, themagnetoresistive stripe is formed to produce a giant magnetoresistiveeffect. In a further advantageous embodiment, the magnetoresistivestripe is formed to produce an anisotropic magnetoresistive effect, acolossal magnetoresistive effect, or a tunnel magnetoresistive effect.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, identical reference symbols generally designate the sameor substantially identical component parts throughout the various views.In the description below, various exemplary embodiments of the inventionare described with reference to the following drawings, in which:

FIG. 1 illustrates a cross-sectional drawing of a magnetoresistivedevice, constructed according to the principles of the invention;

FIG. 2 illustrates a cross-sectional drawing of a magnetoresistivedevice formed as a magnetoresistive stripe with a via to produce a locallateral short circuit, constructed according to the principles of theinvention;

FIG. 3 illustrates a graph showing the ratio of the overall conductivityof a magnetoresistive structure containing local lateral short circuitregions, constructed according to the principles of the invention, tothe overall conductivity of a GMR structure without local lateral shortcircuit regions;

FIG. 4 illustrates a plan-view drawing of a magnetoresistive structure,constructed according to the principles of the invention, for sensing anangular orientation of an externally applied magnetic field;

FIG. 5 illustrates the current distribution along a representative lineof the device as determined by simulation of the device illustrated inFIG. 4;

FIG. 6 illustrates a plan-view graphical representation of sensor layermagnetization of a magnetoresistive sensor formed without localshort-circuit structures;

FIG. 7 illustrates a graph showing the simulated behavior of anisotropyerror and the associated normalized magnetoresistance;

FIG. 8 illustrates a graph showing the simulated behavior of anisotropyerror and the associated normalized magneto resistance as a function oflocal short-circuit structure distance at a fixed local short-circuitstructure length;

FIG. 9 illustrates a plan-view drawing of a magnetoresistive structure,constructed according to the principles of the invention, that can beadvantageously employed for rotary speed sensing;

FIG. 10 illustrates the current distribution of the device illustratedin FIG. 9 along a representative line of the device as determined bysimulation;

FIGS. 11A-11D illustrate plan-view drawings of exemplary constructionsof local short-circuit structures, constructed according to theprinciples of the invention;

FIG. 12A illustrates a plan-view drawing of an anisotropicmagnetoresistive device, constructed according to the principles of theinvention, with three barber-pole stripes oriented at an angle of 45°with respect to the device length axis;

FIG. 12B illustrates a plan-view drawing showing the resulting currentdirection distribution obtained by a two-dimensional simulation of thedevice illustrated in FIG. 12A;

FIG. 13A illustrates a plan-view schematic drawing of an xMR stripe withnecking, constructed according to the principles of the invention;

FIG. 13B illustrates a plan-view schematic drawing of serially connectedxMR elements with limited contact areas, constructed according to theprinciples of the invention; and

FIG. 14 illustrates schematically a current distribution in an xMRelement that is constructed with a small ratio of contact-to-contactdistance to structure width.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Current designs of xMR sensor structures are generally formed with longlength-to-width ratio to obtain a CIP (current-in-plane) circuitconfiguration with sufficiently high electrical resistance so that itcan be readily employed for signal processing without the need for ahigh gain voltage-sensing current. In a typical xMR sensor application,a signal is sensed by applying a known current to an xMR device andsensing the voltage produced across the xMR device with an operationalamplifier.

The current distribution over the structural width of an xMR device isgenerally uniform, i.e., all regions of the structure contributeapproximately equally to its magnetoresistance. From a magnetic fieldsensing point of view, it would be advantageous to underweight and/or tooverweight the current density in certain regions of the xMR structure.For example, for angle-sensing applications, edge regions of astripe-shaped xMR structure exhibit high shape anisotropy, resulting inan angle-sensing error. If current flow in the edge regions was reducedand/or current flow in the middle region of the xMR stripe wasincreased, the angular field-sensing accuracy would be improved. Ofcourse, a further increase of the structure width would also lead tooverweighting of current flow in the central region of the devicecompared to the edge areas, leading to a reduced angular field-sensingerror. The increase in xMR active area is not acceptable for manyapplications from a cost perspective. For rotational speed-sensingapplications, high anisotropy of free layer magnetization is required.Since the minimum width of the xMR structure is limited by the etchingprocess, a shift of the main current to the edge regions would lead tobetter sensor performance without approaching an etching limit of amanufacturing process.

In an xMR sensor structure, constructed according to the principles ofthe invention, the current distribution within an xMR sensor is modifiedby “local short-circuit” (LSC) structures to obtain improved sensorperformance. Furthermore, an integration concept is introduced followingthe principles of the invention that provides LSC structures that arefully compatible with CMOS fabrication, and which do not introduceadditional processing steps. The size of the resulting LSC structuresadvantageously can be very small, and are scalable with the generationof the technology used for xMR sensor production.

Further description of a process for monolithic integration of xMRstructures that are fully compatible with current CMOS mass-productionprocesses are provided by Kolb, et al., in U.S. patent application Ser.No. 11/360,538, Publication Number US 2006/0202291 A1, entitled“Magnetoresistive Sensor Module and Method for Manufacturing the Same,”which is hereby incorporated herein by reference.

Turning now to FIG. 1, illustrated is a cross-sectional drawing of anxMR magnetoresistive device 100, constructed according to the principlesof the invention. The magnetoresistive device includes conductive viasto an underlying conductive layer to alter a current flow within themagnetoresistive structure to improve its position- or angle-sensingcharacteristics. The xMR magnetoresistive structure is formed on asubstrate 101, which can be, without limitation, a silicon or compoundsemiconductor substrate such as commonly used to form an integratedcircuit, and may include active and/or passive integrated circuitcomponents. Above the substrate an insulating layer 102, such as asilicon dioxide layer, is deposited. A patterned, conductive layerforming interconnect structures, such as conductive structure 103, areformed above insulating layer 102. A further insulating layer 104 isdeposited above the patterned, conductive layer. A magnetoresistivedevice 105, such as a GMR magnetoresistive device, is formed aboveinsulating layer 104. Conductive via structures are formed in insulatinglayer 104 to provide interconnections between magnetoresistive device105 and the patterned, conductive layer that was formed therebelow. Theconductive via structures comprise a conductive material 108 such astungsten deposited in apertures of the insulating layer 104. In apreferred embodiment, a conductive film 106 is optionally deposited inthe apertures to form a liner prior to filling with the conductivematerial. A passivating layer 107 for the structure, such as an oxide,nitride, or polyimide layer, is formed above magnetoresistive device105. Techniques to form and pattern such layers and structures asdescribed hereinabove are well known in the art and will not bedescribed in further detail in the interest of brevity. Thus, asillustrated in FIG. 1, a contact concept is introduced for therealization of local lateral short circuit (LSC) structures to alter acurrent distribution in a magnetoresistive device.

Turning now to FIG. 2, illustrated is a cross-sectional drawing of aportion of a magnetoresistive device formed as a GMR stripe with a viastructure of width d_(VIA) beneath a region of the stripe to produce alocal lateral short circuit, constructed according to the principles ofthe invention. The via is formed with a via-filling material (e.g.,tungsten, “W”) deposited within an optional via film, and a conductivemetal structure (e.g., aluminum, “Al”) beneath it. The sheet resistanceof the xMR layer is thereby significantly reduced in the region aroundthe via for in-plane currents by the high conductivity of the metallicvia structures formed thereunder. Elements in FIG. 2, as in otherfigures, with the same reference designation used in an earlier figurewill not be redescribed in the interest of brevity.

In order to evaluate the increase of conductivity in such a regionproduced by underlying vias coupled to a metal structure,two-dimensional electrical simulations were performed for structuressuch as illustrated in FIG. 2. The tungsten for the via filling had athickness of 400 nm, and aluminum in the underlying metal had athickness of 500 nm, which are typical thickness values for variousapplications. The conductivity of the tungsten was assumed to be 14times higher than the GMR conductivity, and the conductivity of thealuminum was assumed to be 30 times higher. Via width, d_(VIA), wasassumed to be 0.25 μm. The simulation indicated that most of the currentflows through the GMR, through the tungsten-filled vias, and through theunderlying aluminum metal. Only a few carriers reach the bottom aluminumlayer, since the via width is too small to allow the electrical field toextend substantially over the entire LSC structure. Consequently, theLSC has a four-times higher conductivity than the GMR layer, which isjudged to be a moderate increase in conductivity.

A two-dimensional simulation was then performed for the currentdistribution within the GMR layer with a via width of 5 μm. The tungstenthickness was 400 nm, and the aluminum thickness was 500 nm. It wasobserved that increasing the width of the via leads to an extension ofthe electric field substantially throughout the LSC structure, resultingin a significant contribution by the aluminum portion of the structureto its conductivity. In this case, where the width of the via structured_(VIA) is 5 μm, the conductivity of the LSC region is about 35 timeshigher than the GMR conductivity, which is judged to be a significantincrease.

Turning now to FIG. 3, illustrated is the ratio σ_(VIA)/σ_(GMR) of theoverall conductivity, σ_(VIA), of a GMR structure containing locallateral short circuit regions to the overall conductivity, σ_(GMR), of aGMR layer without local lateral short circuit regions. This ratio isplotted on the vertical axis of the figure against via width with alogarithmic scale on the horizontal axis. The conductivity ratio is ameasure of the short circuit efficiency of the LSC structure. FIG. 3illustrates a correlation between LSC width and the short circuitefficiency of a LSC structure for the case of a 400-nm thick tungstenvia and underlying 500 nm thick aluminum metal. For via sizes greaterthan 0.7 μm, a 10 times higher local conductivity advantageously can beachieved. Using other via filling materials with higher conductivity(e.g., Cu) can further increase the conductivity efficiency of the LSCstructure.

The implementation of LSC structures to modify the current distributionin a magnetoresistive structure will be described with several examples.

In a first example, the influence of LSC structures for angle-sensingdevices will be described. Turning now to FIG. 4, illustrated is aplan-view drawing of an xMR structure for sensing an angular orientationof an externally applied magnetic field. The xMR sensor stripe 401,without limitation, has a width of 10 μm and a length of 30 μm. Thesmall black regions, 402 and 403, at the top and bottom edges,respectively, of the xMR sensor stripe represent low-resistance contactareas ensuring current injection mainly in the mid region of the stripe.The LSC structures, such as LSC structure 404, are formed in the middleof the sensor stripe, with a length l_(LSC) and a separation distanced_(LSC).

Simulation of the current distribution for the structure illustrated inFIG. 4 demonstrated that substantial nonuniformity of current flowresults due to the combination of local current injection in the midregion of the xMR structure and the mid-region implementation of highlyconductive LSC structures. Exemplary simulations were performed for thecase where l_(LSC)=1.1 μm, and d_(LSC)=2.2 μm, and LSC conductivityassumed to be 100 times higher than that of the xMR material. The xMRstructure width was 10 μm, and its length, 30 μm. As a result ofinclusion of local LSC structures, the current density between the LSCstructures in the mid-region area is enhanced compared to the currentdensity in the edge regions.

FIG. 5 illustrates the current distribution determined by a simulationof the device illustrated in FIG. 4 at the location of the dashed line405 for the exemplary conditions described in the preceding paragraph.In this simulation example, the current density in the mid-region of thestructure is about 27% higher than that at edge regions of thestructure. Thus, local LSC structures, constructed according to theprinciples of the invention, are advantageously employed to enhance theperformance of a position-sensing xMR device.

Turning now to FIG. 6, illustrated is a plan-view schematicrepresentation of sensor layer magnetization of an xMR sensor accordingto micromagnetic simulations. It can be seen in FIG. 6 that magneticdomains at the edges of the stripe are not well aligned with thedirection of the externally applied magnetic field. The magnetic domainsin the mid-region of the structure are better aligned. The reason forthe misalignment at the edges is shape anisotropy, which is typicallystrongest at the edges of a structure. If the current density is uniformover the stripe width, all magnetic domains contribute accurately to thexMR signal. As a result of nonuniformity, the regions at the edge of thestructure produce a deviation of the sensed angle of the externallyapplied magnetic field, i.e., an error, referred to as an “anisotropyangle error,” is produced. Furthermore, an additionalhysteresis-originated error can also occur. Hysteresis describes theeffect of a history-dependent internal magnetization of a ferromagneticlayer upon an external magnetic field, i.e., the internal magnetizationdepends on the manner in which a certain magnetic field direction isapplied. A reduction of the contribution of the edge regions to the xMRsignal would therefore reduce the anisotropy- and hysteresis-inducedcomponents of the angular error. A shifted current distribution can thusenhance the performance of an angle-sensing xMR device.

Turning now to FIG. 7, illustrated is a graph showing the simulatedbehavior of anisotropy error (on the left vertical axis of the graph)and the associated, normalized xMR resistance (“xMR signal in r.u.,relative units” on the right vertical axis of the graph). The graph isconstructed as a function of LSC structure length for the exemplary casewhen the inter-via distance is kept constant at d_(LSC)=3.36 μm. Theconductivity of the LSC structure as a function of length was chosenaccording to the numerical findings illustrated in FIG. 4. Without anyLSC structures (i.e., l_(LSC)=0 μm) and uniform current injection overthe whole width of the stripe, a maximum anisotropy error of 0.7° isobserved. The inclusion of LSC structures with length increased up to 14μm leads to a continuous decrease in angular error down to 0.52° for anLSC length of 13.4 μm. Simultaneously, the xMR resistance decreases byabout 35% (on a relative basis) since the regions where the LSCstructures are located do not contribute to the xMR signal. Portions ofthe xMR stripe are effectively shorted by the LSC structures. However,in most cases, the gain in sensor performance is more important than thereduction of xMR device resistance. Further stack improvement can bemade to compensate for the reduction of xMR device resistance due to theLSC structures. Another possibility to compensate for the loss of xMRdevice resistance is to lengthen the xMR structure.

Turning now to FIG. 8, illustrated is a graph showing the simulatedbehavior of anisotropy error and the associated, normalized xMRresistance (“signal”) as a function of LSC structure distance at a fixedLSC structure length of d_(LSC)=2.8 μm. For increased LSC structuredistance at a fixed LSC structure length, the anisotropy error isminimum at minimum distance, and increases for larger distances. Whenthe distance between the LSC structures increases, the charge carriersextend to the outer edges of the structure. This results in a growingelectrical influence of the edge regions on device resistance.Accordingly, the xMR signal increases.

Besides angular sensors, rotary speed sensors can also derive benefitfrom a nonuniform current distribution. For rotary speed sensing, highshape anisotropy can be employed to produce a wide linear transitionregion from a low- to a high-resistance state. Narrowing of the xMRstripe leads to an increase in shape anisotropy, but from amanufacturing point of view, it is more difficult to employ an etchprocess for small structure sizes with suitably low cost andreproducibility.

Turning now to FIG. 9, illustrated is a plan-view drawing of an xMRstructure, constructed according to the principles of the invention,that can be advantageously employed for rotary speed sensing. The xMRstructure includes xMR stripe 901, low-resistance contact areas 902 and903, and LSC structure 904. In an exemplary embodiment, the xMR devicestripe width is 2 μm, and the length, 30 μm. Implementation of LSCstructures along sidewalls of the xMR device provides local currentinjection to improve field-sensing accuracy.

The implementation of an LSC structure as illustrated in FIG. 9 producesa nonuniform current distribution, with the major portion of thecarriers localized at the edges of the device. Simulation was performedof an exemplary xMR structure with l_(LSC)=1.1 μm and d_(LSC)=1.1 μm,and LSC conductivity assumed to be 100 times higher than that of the xMRmaterial. The xMR structure width was 2 μm, and its length, 30 μm.Examination of current flow at dashed line 905 in FIG. 9 shows currentat the edges of the xMR stripe for this example to be approximately 35%higher than that at the mid-region of the stripe. As a consequence, theelectrical contribution of the mid-region of the device having a lowershape anisotropy effect to the xMR resistance is reduced, leading toenhancement of the linear transition range in this exemplary structureby about 7%. Concurrently, the xMR resistance is reduced by about 27%.

Turning now to FIG. 10, illustrated is the current distribution of FIG.9 along the dashed line 905. In the edge regions of the stripe, thecurrent is about 35% higher than that in the mid-region of the stripe.

Turning now to FIGS. 11A-11D, illustrated, respectively, are plan-viewdrawings of exemplary constructions of local short-circuit structures.In FIGS. 11A-11D, 1101 represents a portion of an xMR stripe. A via isrepresented by reference designation 1108, and an underlying conductivemetal structure is represented by reference designation 1103. FIG. 11Aillustrates a via with a laterally extended width. FIG. 11B illustratesa plurality of square vias to form a short circuit stripe with narrowervia widths. FIG. 11C illustrates a plurality of vias with laterallyextended width. And FIG. 11D illustrates a plurality of square vias toform a short circuit stripe with a width that is independent of viasize. These examples demonstrate, without limitation, different possibleLSC constructions. If the width of a via produces a short circuit whichis high enough for the application, then the length of the LSC structurecan be determined by a long via, as illustrated in FIG. 11A, or by aplurality of square vias, as illustrated in FIG. 11B. In the event thathigh short circuit efficiency is required, a plurality of LSC elementsconnected by an underlying metal layer can be used, as illustrated inFIG. 11B and FIG. 11D. Beyond the linear configurations of LSCsillustrated in these figures, further shapes and orientations arepossible within the broad scope of the invention.

A further application of LSC structures, constructed according to theprinciples of the invention, incorporates so-called “barber-pole”structures, which are well known for anisotropic magnetoresistive (AMR)sensors. The “barber-pole” structures refer to the use of stripes ofhighly conductive material located with a certain angle with respect tothe AMR length axis, and are conventionally deposited on an externalsurface of an AMR sensor. By including a highly conductive material atan angle with respect to the AMR length axis, the current direction inthe region between two barber-pole structures can be determinedindependently of the direction of an externally applied voltage. The useof barber-pole stripes can be useful for building AMR sensors, since theAMR effect depends on the angle between the current and magnetizationdirection. For some sensor applications, it is preferable to provide acurrent direction in the xMR device which is not perpendicular to thegradient of an externally applied electrical potential. In currentpractice, the barber-pole structures are placed on top of the AMR layerof the structure by additional processing steps which are not fullycompatible with current state-of-the-art mass production processes.Barber-pole structures built of LSC structures formed with vias coupledto an underlying metallic layer, constructed according to the principlesof the invention, do not have these disadvantages.

Turning now to FIG. 12A, illustrated is a plan-view drawing of an AMRstructure, constructed according to the principles of the invention,with three barber-pole stripes oriented at an angle of 45° with respectto the AMR length axis. Of course, a different number of barber-polestripes can also be used. The AMR structure includes a stripe 1201 of asuitable magnetoresistive material. A magnetic material sometimesemployed for construction of an AMR structure is Permalloy. Electricallyconductive barber-pole stripes, such as barber-pole stripe 1208, areformed below the surface of the magnetoresistive material atapproximately a 45° angle with respect to the length axis of the AMRstructure. The embedded conductive barber-pole stripes are coupled tothe overlying magnetoresistive material by via structures (not shown),constructed as previously described hereinabove. Top and bottomelectrically conductive contacts, 1202 and 1203, respectively, providecontacts for application of a potential difference, V1−V2, so that acurrent through the structure can be sensed. Alternatively, a knowncurrent is supplied through contacts 1202 and 1203, and the resultingpotential difference is sensed. The electrical conductivity of theembedded barber-pole material is assumed, without limitation, to be 20times higher then the AMR conductivity. An exemplary AMR stripe width is10 μm.

Turning now to FIG. 12B, illustrated is a plan-view drawing showing theresulting current direction distribution obtained by a two-dimensionalelectrical numerical simulation. Without barber-pole stripes, thecurrent direction would be oriented from top to bottom, perpendicular tothe potential difference V1−V2. With barber-pole stripes, the directionof internal current flow is realigned to be generally perpendicular tothe barber-pole stripe axes. As a result, the barber-pole stripes act aslocal short-circuit structures, forcing the current to flow between thebarber pole stripes at an angle of 45° with respect to the length axisof the AMR structure.

Turning now to FIG. 13A, illustrated is a plan-view schematic drawing ofan xMR stripe 1301 with a necking region 1302, resulting in a single,subdivided xMR element connected by xMR material. The xMR stripe 1301includes vias, such as via 1308, and metal contacts, such as metalcontact 1303. Beneath the necking, a local short-circuit structure isplaced, which extends into the xMR structure. A non-homogeneous currentdistribution can be produced by selection of the shape of the xMRstructure in combination with the LSC structure configuration. When thedistance between LSC structures is smaller than the width of the xMRstructure, a non-homogeneous current distribution results throughout thexMR structure. A typical advantageous configuration, without limitation,would be a ratio of the inter-LSC structure distance to xMR structurewidth that is less than three. The shape of the subdivided xMR elementscan be, without limitation, square, rectangular, rhombic, circular, orelliptic.

Turning now to FIG. 13B, illustrated is a plan-view schematic drawing ofserially connected xMR elements with limited contact areas. Each xMRelement, such as xMR element 1311, includes vias, such as via 1318, andmetal contacts, such as metal contact 1313. A non-homogeneous currentdistribution can be produced by selection of the shape of the xMRstructure in combination with the contact configuration. When thecontact-to-contact distance D is smaller than the width W of thestructure, a non-homogeneous current distribution results throughout thestructure. A typical xMR element configuration, without limitation,would be a ratio of the contact-to-contact distance to structure widththat is less than three. A single sensor element could then beadvantageously constructed as a series-connected arrangement of suchsingle xMR elements. The shape of the single xMR elements can be,without limitation, square, rectangular, rhombic, circular, or elliptic.

Turning now to FIG. 14, illustrated is a drawing illustratingschematically a current distribution in an xMR element that isconstructed with a small ratio of contact-to-contact distance tostructure width. The thickness of the arrows in the drawing is a measureof the current density, indicating the lack of homogeneity of thecurrent flow that can be produced by the shape of the xMR structure incombination with the contact configuration.

A magnetoresistive device has thus been described that may be used tosense an externally applied magnetic field. In accordance with oneexemplary embodiment of the invention, the magnetoresistive deviceincludes a magnetoresistive stripe with vias forming local shortcircuits between the magnetoresistive stripe and an underlying metalliclayer. In an advantageous embodiment, an electrically conductive,patterned metallic layer is formed to produce electrically isolatedconductive regions over a substrate, and an insulating layer is formedor deposited over the patterned metallic layer. In an advantageousembodiment, the metallic layer comprises aluminum. In an advantageousembodiment, the substrate comprises, without limitation, silicon or acompound semiconductor material such as gallium arsenide. In anadvantageous embodiment, the insulating layer comprises, withoutlimitation, silicon dioxide. The magnetoresistive stripe is formed ordeposited over the insulating layer, and a plurality of conductive viascouple electrically isolated conductive regions of the metallic layer tothe magnetoresistive stripe. In an advantageous embodiment, themagnetoresistive stripe comprises Permalloy. In an advantageousembodiment, the magnetoresistive stripe is formed or configured toproduce a giant magnetoresistive effect. In a further embodiment, themagnetoresistive stripe is formed or configured to produce ananisotropic magnetoresistive effect, a colossal magnetoresistive effect,or a tunnel magnetoresistive effect. In a further advantageousembodiment, a plurality of conductive vias forms local short circuitsbetween the magnetoresistive stripe and an electrically isolated regionof the metallic layer. In an advantageous embodiment, the vias comprisetungsten, but other electrically conductive materials can be used. In afurther advantageous embodiment, electrically conductive contacts areformed or deposited at opposing ends of the magnetoresistive stripe toenable an electrical potential difference to be applied to themagnetoresistive stripe. In a further advantageous embodiment, themetallic layer is formed as electrically conductive stripes oriented atapproximately a 45° angle with respect to an axis of themagnetoresistive stripe. Of course, other angles of orientation ofstripes formed in the metallic layer may be employed for a particularapplication.

Another exemplary embodiment of the invention provides a method offorming a magnetoresistive device that may be used to sense anexternally applied magnetic field. In the method, the magnetoresistivedevice is formed with vias to produce local short circuits between amagnetoresistive stripe and an underlying metallic layer. In accordancewith one exemplary embodiment, the method includes forming anelectrically conductive, patterned metallic layer over a substrate toproduce electrically isolated conductive regions, and forming aninsulating layer over the patterned metallic layer. In an advantageousembodiment of the method, the metallic layer comprises aluminum. In anadvantageous embodiment of the method, the substrate comprises siliconor a compound semiconductor material such as gallium arsenide. In anadvantageous embodiment of the method, the insulating layer comprisessilicon dioxide. In an advantageous embodiment, the method includesforming the magnetoresistive stripe over the insulating layer, andcoupling the plurality of electrically isolated conductive regions ofthe metallic layer to the magnetoresistive stripe with conductive viasformed between the metallic layer and the magnetoresistive stripe. In anadvantageous embodiment of the method, the magnetoresistive stripecomprises Permalloy. In an advantageous embodiment, the method includesforming the magnetoresistive stripe to produce a giant magnetoresistiveeffect. In a further embodiment, the method includes forming themagnetoresistive stripe to produce an anisotropic magnetoresistiveeffect, a colossal magnetoresistive effect, or a tunnel magnetoresistiveeffect. In a further advantageous embodiment, the method includesforming a local short circuit between the magnetoresistive stripe and anelectrically isolated region of the metallic layer by forming aplurality of conductive vias in the insulating layer between themagnetoresistive stripe and the electrically isolated region of theunderlying metallic layer. In an advantageous embodiment of the method,the vias comprise tungsten, but other electrically conductive materialscan also be used. In a further advantageous embodiment, the methodincludes forming electrically conductive contacts at opposing ends ofthe magnetoresistive stripe to enable an electrical potential differenceto be applied to the magnetoresistive stripe. In a further advantageousembodiment, the method includes forming the metallic layer aselectrically conductive stripes oriented at approximately a 45° anglewith respect to an axis of the magnetoresistive stripe. Of course, otherangles of orientation of stripes formed in the metallic layer may beemployed for a particular application.

Another exemplary embodiment of the invention provides amagnetoresistive device formed on a metallic layer. A magnetoresistivestripe comprising xMR elements connected by small necking regions aredeposited on an insulating layer deposited on the metallic layer, and aplurality of conductive vias are formed in the insulating layer tocouple the electrically isolated and electrically conductive contactsformed in the metallic layer to the magnetoresistive stripe around thenecking region. A ratio of a diameter of the xMR element to a separationdistance between the vias is less than three to produce a substantiallyinhomogeneous current flow within the magnetoresistive stripe. In afurther advantageous embodiment, a necking region is formed in themagnetoresistive stripe, wherein a local short circuit is formedextending into the magnetoresistive stripe.

Another exemplary embodiment of the invention provides amagnetoresistive device formed on a substrate. A metallic layer isdeposited on the substrate to form electrically isolated andelectrically conductive contacts, and an insulating layer is depositedon the metallic layer. A magnetoresistive stripe is deposited on theinsulating layer, and a plurality of conductive vias are formed in theinsulating layer to couple the electrically isolated and electricallyconductive contacts formed in the metallic layer to the magnetoresistivestripe. A ratio of a diameter of the single xMR element to a separationdistance between the vias is less than three to produce a substantiallyinhomogeneous current flow within the magnetoresistive stripe.

Although a magnetoresistive device has been described for application tosensing an externally applied magnetic field to sense a location, speed,or an orientation of an object, it should be understood that otherapplications of magnetoresistive devices are contemplated within thebroad scope of the invention, and need not be limited to sensing alocation, speed, or an orientation of an object.

Although the invention has been shown and described primarily inconnection with specific exemplary embodiments, it should be understoodby those skilled in the art that diverse changes in the configurationand the details thereof can be made without departing from the essenceand scope of the invention as defined by the claims below. The scope ofthe invention is therefore determined by the appended claims, and theintention is for all alterations that lie within the range of themeaning and the range of equivalence of the claims to be encompassed bythe claims.

1. A magnetoresistive device, comprising: a substrate; a metallic layerincluding electrically isolated regions formed over said substrate; aninsulating layer formed over said metallic layer; a magnetoresistivestripe formed over said insulating layer; and a plurality of conductivevias coupling said electrically isolated regions of said metallic layerto said magnetoresistive stripe, the plurality of conductive vias andmetallic layler forming local lateral short circuit (LSC) structuresalong a length of the magnetoresistive stripe.
 2. The magnetoresistivedevice as claimed in claim 1, wherein said magnetoresistive stripe isconfigured to produce a giant magnetoresistive effect.
 3. Themagnetoresistive device as claimed in claim 1, wherein saidmagnetoresistive stripe comprises Permalloy, said substrate comprisessilicon, said insulating layer comprises silicon dioxide, said viascomprise tungsten, and said metallic layer comprises aluminum.
 4. Themagnetoresistive device as claimed in claim 1, further includingelectrically conductive contacts formed at opposing ends of saidmagnetoresistive stripe.
 5. The magnetoresistive device as claimed inclaim 1, wherein said metallic layer comprises stripes formed atapproximately a 45° angle with respect to an axis of saidmagnetoresistive stripe.
 6. A method of forming a magnetoresistivedevice, the method comprising: forming and patterning a metallic layerwith electrically isolated regions over a substrate; depositing aninsulating layer over said metallic layer; forming apertures in saidinsulating layer above said metallic layer; depositing an electricallyconductive material in said apertures in contact with said electricallyisolated regions to form vias; and forming a magnetoresistive stripeover said insulating layer in electrical contact with said electricallyconductive material, wherein said electrically conductive material andsaid metallic layer form local lateral short circuit (LSC) structuresalong a length of the magnetoresistive stripe.
 7. The method as claimedin claim 6, including forming said magnetoresistive stripe to produce agiant magnetoresistive effect.
 8. The method as claimed in claim 6,wherein said magnetoresistive stripe comprises Permalloy, said substratecomprises silicon, said insulating layer comprises silicon dioxide, saidvias comprise tungsten, and metallic layer comprises aluminum.
 9. Themethod as claimed in claim 6, further including forming electricallyconductive contacts at opposing ends of said magnetoresistive stripe.10. The method as claimed in claim 6, further including forming saidmetallic layer as metallic stripes at approximately a 45° angle withrespect to an axis of said magnetoresistive device.
 11. Amagnetoresistive device, comprising: a substrate; a metallic layerincluding electrically isolated regions deposited on said substrate; aninsulating layer deposited on said metallic layer; a magnetoresistivestripe deposited on said insulating layer; and a plurality of conductivevias coupling said electrically isolated regions of said metallic layerto said magnetoresistive stripe, the plurality of conductive vias andmetallic layer forming local lateral short circuit (LSC) structuresalong a length of the magnetoresistive stripe.
 12. The magnetoresistivedevice as claimed in claim 11, wherein said magnetoresistive stripe isconfigured to produce a giant magnetoresistive effect.
 13. Themagnetoresistive device as claimed in claim 11, wherein said pluralityof conductive vias form a local short circuit between saidmagnetoresistive stripe and said metallic layer.
 14. Themagnetoresistive device as claimed in claim 11, wherein saidmagnetoresistive stripe comprises Permalloy.
 15. The magnetoresistivedevice as claimed in claim 11, further including electrically conductivecontacts formed at opposing ends of said magnetoresistive stripe.
 16. Amagnetoresistive device, comprising: a substrate; a metallic layerdeposited on said substrate to form electrically isolated andelectrically conductive contacts; an insulating layer deposited on saidmetallic layer; a magnetoresistive stripe deposited on said insulatinglayer; and a plurality of conductive vias coupling said electricallyisolated and electrically conductive contacts formed in said metalliclayer to said magnetoresistive stripe, wherein a ratio of a diameter ofsaid magnetoresistive stripe to a separation distance between said viasis less than three.
 17. The magnetoresistive device as claimed in claim16, wherein said magnetoresistive stripe is configured to produce agiant magnetoresistive effect.
 18. The magnetoresistive device asclaimed in claim 16, wherein said magnetoresistive stripe comprisesPermalloy.
 19. The magnetoresistive device as claimed in claim 16,wherein said electrically isolated and electrically conductive contactsare formed at opposing ends of said magnetoresistive stripe.
 20. Themagnetoresistive device as claimed in claim 16, further comprising anecking region formed in said magnetoresistive stripe, wherein a localshort circuit structure is formed extending into said magnetoresistivestripe.
 21. The magnetoresistive device as claimed in claim 16, whereinsaid substrate comprises silicon, said insulating layer comprisessilicon dioxide, said vias comprise tungsten, and said metallic layercomprises aluminum.
 22. A magnetoresistive device, comprising: asubstrate; a metallic layer including electrically isolated regionsformed over said substrate; an insulating layer formed over saidmetallic layer; a magnetoresistive stripe formed over said insulatinglayer; and a plurality of conductive vias coupling said electricallyisolated regions of said metallic layer to said magnetoresistive stripe,wherein said magnetoresistive stripe comprises Permalloy, said substratecomprises silicon, said insulating layer comprises silicon dioxide, saidvias comprise tungsten, and said metallic layer comprises aluminum. 23.A magnetoresistive device, comprising: a substrate; a metallic layerincluding electrically isolated regions formed over said substrate; aninsulating layer formed over said metallic layer; a magnetoresistivestripe formed over said insulating layer; and a plurality of conductivevias coupling said electrically isolated regions of said metallic layerto said magnetoresistive stripe, wherein said metallic layer comprisesstripes formed at approximately a 45° angle with respect to an axis ofsaid magnetoresistive stripe.
 24. The magnetoresistive device as claimedin claim 1, wherein the LSC structures cause a non-uniform currentdistribution along a width of the magnetoresistive stripe; and a sensingaccuracy of the magnetoresistive stripe with non-uniform current densityis higher than a sensing accuracy of the magnetoresistive stripe with auniform current density.
 25. The magnetoresistive device as claimed inclaim 1, wherein the LSC structures are disposed at a center of themagnetoresistive stripe.
 26. The magnetoresistive device as claimed inclaim 1, wherein the LSC structures are disposed along edges of themagnetoresistive stripe.